U.S. patent number 8,561,776 [Application Number 13/430,830] was granted by the patent office on 2013-10-22 for imaging unit and coin identifying apparatus.
This patent grant is currently assigned to Laurel Precision Machines Co., Ltd.. The grantee listed for this patent is Naofumi Mirumachi, Masao Mori, Masataka Takahashi. Invention is credited to Naofumi Mirumachi, Masao Mori, Masataka Takahashi.
United States Patent |
8,561,776 |
Mirumachi , et al. |
October 22, 2013 |
Imaging unit and coin identifying apparatus
Abstract
An imaging unit images a subject having an unevenness pattern on
a surface. The imaging unit includes: a surface light source that
emits with a constant output illumination light illuminating the
surface of the subject; an imager that receives reflected light
reflected by the surface of the subject; and a beam splitter that
is arranged at a location at which the illumination light emitted
from the surface light source and the reflected light incident on
the imager intersect with each other. The illumination light
emitted from the surface light source is incident on the surface of
the subject via the beam splitter. The reflected light reflected by
the surface of the subject is incident on the imager via the beam
splitter. The illumination light incident on the surface of the
subject includes parallel light that is perpendicularly incident on
the surface of the subject, and diffused light.
Inventors: |
Mirumachi; Naofumi (Saitama,
JP), Mori; Masao (Saitama, JP), Takahashi;
Masataka (Matsudo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Mirumachi; Naofumi
Mori; Masao
Takahashi; Masataka |
Saitama
Saitama
Matsudo |
N/A
N/A
N/A |
JP
JP
JP |
|
|
Assignee: |
Laurel Precision Machines Co.,
Ltd. (Osaka, JP)
|
Family
ID: |
46021995 |
Appl.
No.: |
13/430,830 |
Filed: |
March 27, 2012 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120247918 A1 |
Oct 4, 2012 |
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Foreign Application Priority Data
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Mar 30, 2011 [JP] |
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2011-076340 |
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Current U.S.
Class: |
194/302;
73/163 |
Current CPC
Class: |
G07D
5/005 (20130101) |
Current International
Class: |
G07D
5/00 (20060101); G07D 5/02 (20060101) |
Field of
Search: |
;194/302,328,329,330,332,333 ;453/4 ;73/163 ;382/136 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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20004826 |
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Jun 2000 |
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DE |
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2360138 |
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Feb 1978 |
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FR |
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6-150104 |
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May 1994 |
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JP |
|
9-319911 |
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Dec 1997 |
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JP |
|
11014557 |
|
Jan 1999 |
|
JP |
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2000-331211 |
|
Nov 2000 |
|
JP |
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2001-34804 |
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Feb 2001 |
|
JP |
|
Other References
EP Search Report in EP 12 16 1373 dated Jul. 9, 2012. cited by
applicant .
Korean Office Action mailed Jun. 19, 2013 in Korean Patent
Application No. 10-2012-0031135 and Entlish translation, 7 pp.
cited by applicant.
|
Primary Examiner: Beauchaine; Mark
Attorney, Agent or Firm: Nixon & Vanderhye P.C.
Claims
What is claimed is:
1. An imaging unit that images a subject having an unevenness
pattern on a surface, the imaging unit comprising: a surface light
source that emits with a constant output illumination light
illuminating the surface of the subject; an imager that receives
reflected light reflected by the surface of the subject; and a beam
splitter that is arranged at a location at which the illumination
light emitted from the surface light source and the reflected light
incident on the imager intersect with each other, the illumination
light emitted from the surface light source being incident on the
surface of the subject via the beam splitter, the reflected light
reflected by the surface of the subject being incident on the
imager via the beam splitter, the illumination light incident on
the surface of the subject including parallel light that is
perpendicularly incident on the surface of the subject, and
diffused light, the surface light source including: a light source
element that emits light; a light guide plate that has, on a lower
surface thereof, a prism pattern reflecting the light emitted from
the light source element; the light guide plate emitting, from an
upper surface thereof, the light reflected by the prism pattern;
and a diffusion film that is layered on the upper surface of the
light guide plate, the diffusion film dispersing a portion of the
light emitted from the upper surface to generate the parallel light
and the diffused light.
2. The imaging unit according to claim 1, wherein the diffused
light includes light that is obliquely incident on the surface of
the subject.
3. The imaging unit according to claim 1, wherein the imager
includes a telecentric imaging optics.
4. The imaging unit according to claim 1, wherein the subject is a
coin.
5. A coin identifying apparatus comprising: a conveying unit that
conveys a coin; the imaging unit according to claim 1, the imaging
unit imaging a surface of the coin that is conveyed by the
conveying unit; and an identifying unit that identifies the coin
based on an image acquired by the imaging unit.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an imaging unit and a coin
identifying apparatus.
Priority is claimed on Japanese Patent Application No. 2011-076340,
filed Mar. 30, 2011, the content of which is incorporated herein by
reference.
2. Description of Related Art
There is known a coin identifying apparatus that images a surface
of a coin, and identifies the coin from the unevenness pattern of
the coin surface that appears in the acquired image. That kind of
coin identifying apparatus successively conveys a plurality of
coins on a conveyance route, and when the coins pass an imaging
location that is provided on that conveyance route, that coin is
imaged by the imaging unit. That imaging unit includes a light
source that emits illumination light that illuminates the coin
surface, and an imager that receives the reflected light that is
reflected by the coin surface (see, for example, Japanese
Unexamined Patent Application, First Publication No. H09-319911
(hereinbelow referred to as Patent Document 1) and Japanese
Unexamined Patent Application, First Publication No. H06-150104
(hereinbelow referred to as Patent Document 2)).
In the imaging unit that is disclosed in Patent Document 1, the
light source is arranged away from the normal direction of the coin
surface, and the imager is arranged in the normal direction of the
coin surface. The illumination light that is emitted from the light
source is obliquely incident on the coin surface, and the imager
mainly receives the reflected light that is reflected by the edge
portion of the unevenness pattern of the coin surface. Contrast is
generated between the edge portion of the unevenness pattern of the
coin surface and the other portion in the image that is obtained by
this imaging unit. However, since this imaging unit receives by the
imaging unit the reflected light that has been reflected at the
edge portion of the unevenness pattern of the coin surface, it is
difficult to detect the defaced state and color of the coin
surface.
In the imaging unit that is disclosed in Patent Document 2, a
surface light source that emits parallel light is used as the light
source. The surface light source is arranged in the normal
direction of the coin surface. A half mirror is arranged between
the surface light source and the coin. An imager is arranged in the
optical path of the light beam that advances in the normal
direction of the coin surface and is reflected by the half mirror.
The illumination light (parallel light) that is emitted from the
surface light source passes through the half mirror to be
perpendicularly incident on the coin surface. The imager receives
the reflected light that is mainly reflected by the coin surface
excluding the edge portion of the unevenness pattern, and reflected
by the half mirror. Contrast is generated between the edge portion
of the unevenness pattern of the coin surface and the other portion
in the image that is obtained by this imaging unit. Moreover, it is
also possible to detect the defaced state and color of the coin
surface with this imaging unit.
However, in the imaging unit that is disclosed in Patent Document
2, in the case of the defacement of the coin surface being severe,
or the coin surface being a diffusing surface, the brightness of
the coin surface is overall insufficient. As a result, the contrast
between the edge portion of the unevenness pattern and the other
portion of the coin surface in the acquired image becomes
indistinct, and identification sometimes cannot be performed. As a
solution in such a case, adjusting the output of the light source
in accordance with the nature of the coin surface leads to a drop
in the identification process speed in a coin identifying apparatus
that images a plurality of coins in succession.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an imaging unit
that, while holding constant the output of a light source, can
reliably capture the unevenness pattern of the surface of a subject
without being influenced by the nature of the surface of the
subject. Also an object of the present invention is to provide a
coin identifying apparatus that has excellent identification
processing speed.
An imaging unit according to the present invention images a subject
having an unevenness pattern on a surface. The imaging unit
includes: a surface light source that emits with a constant output
illumination light illuminating the surface of the subject; an
imager that receives reflected light reflected by the surface of
the subject; and a beam splitter that is arranged at a location at
which the illumination light emitted from the surface light source
and the reflected light incident on the imager intersect with each
other. The illumination light emitted from the surface light source
is incident on the surface of the subject via the beam splitter.
The reflected light reflected by the surface of the subject is
incident on the imager via the beam splitter. The illumination
light incident on the surface of the subject includes parallel
light that is perpendicularly incident on the surface of the
subject, and diffused light.
A coin identifying apparatus according to the present invention
includes: a conveying unit that conveys a coin; the above-described
imaging unit imaging a surface of the coin that is conveyed by the
conveying unit; and an identifying unit that identifies the coin
based on an image acquired by the imaging unit.
According to the present invention, an imaging unit emits
illumination light that includes parallel light and diffused light
to a surface of a subject. The brightness of the overall surface of
the substrate is ensured by the diffused light, and thereby the
contrast of the edge portion of the unevenness pattern of the
surface of the substrate and the other portion of the surface of
the substrate that is produced by parallel light becomes distinct.
Thereby, while holding constant the output of a light source, it
can reliably capture the unevenness pattern of the surface of the
subject without being influenced by the nature of the surface of
the subject. Moreover, according to a coin identifying apparatus
that includes the imaging unit, it is possible to keep the
identification processing speed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows one example of a coin identifying apparatus for
describing an embodiment of the present invention.
FIG. 2 is a block diagram showing an identification system of the
coin identifying apparatus in FIG. 1.
FIG. 3 shows an imaging unit of the coin identifying apparatus in
FIG. 1, being an example of an imaging unit for describing the
embodiment of the present invention.
FIG. 4 shows an example of a surface light source of the imaging
unit in FIG. 3.
FIG. 5 schematically shows the illumination light that is incident
on the surface of a coin, and the reflected light that is reflected
by the surface of the coin.
FIG. 6 shows a modification example of the imaging unit in FIG.
3.
FIG. 7 shows another example of the imaging unit for describing the
embodiment of the present invention.
FIG. 8A shows a first brightness distribution of an image that is
obtained by imaging the surface of a coin.
FIG. 8B shows a second brightness distribution of an image that is
obtained by imaging the surface of a coin.
FIG. 8C shows a third brightness distribution of an image that is
obtained by imaging the surface of a coin.
FIG. 8D shows a fourth brightness distribution of an image that is
obtained by imaging the surface of a coin.
FIG. 9 shows the illuminance distribution of the illumination light
when imaging images with the brightness distributions of FIGS. 8A
to 8D.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an example of a coin identifying apparatus according
to an embodiment of the present invention. FIG. 2 is a block
diagram showing an identification system of the coin identifying
apparatus shown in FIG. 1.
The coin identifying apparatus shown in FIG. 1 and FIG. 2 includes
a conveying unit 3, a detecting unit 4, an imaging unit 5, and an
identifying unit 6. The conveying unit 3 conveys a coin 2. The
detecting unit 4 detects the coin 2 that is conveyed. The imaging
unit 5 images a surface of the coin 2 that is conveyed. The
identifying unit 6 identifies the coin 2 based on the image that is
acquired by the imaging unit 5.
The conveying unit 3 includes a conveying table 10, a pair of
pulleys 11, and an endless belt 12. The conveying table 10
specifies the conveying path of the coins 2. The endless belt 12 is
mounted on the pair of pulleys 11. The pair of pulleys 11 are
respectively arranged at both end portions of the conveying table
10 in the extending direction of the conveying table 10, and are
driven by a motor not illustrated. The endless belt 12 is arranged
facing the conveying table 10. A space between the endless belt 12
and the conveying table 10 is set to be able to suitably take in
the coin 2.
The conveying table 10 has a one end portion 10a (hereinbelow
referred to as the upstream side end portion) and the other end
portion 10b (hereinbelow referred to as the downstream side end
portion). The position of the upstream side end portion 10a
corresponds to the upstream side of the conveying path. The
position of the downstream side end portion 10b corresponds to the
downstream side of the conveying path. A plurality of coins that
are inserted into a coin slot, not illustrated, of the coin
identifying apparatus 1 are successively supplied to the upstream
side end portion 10a. The endless belt 12 is rotationally driven at
a constant speed by the motor and the pair of pulleys 11. The coins
2 that are supplied to the upstream side end portion 10a on the
conveying table 10 are caught in the space between the endless belt
12, and the transport table 10. Those coins 12 move on the
conveying table 10 while being dragged by the endless belt 12 by
the friction with the endless belt 12, and are conveyed to the
downstream side end portion 10b of the conveying table 10 along the
conveying path.
The imaging unit 5 is arranged on the lower surface side of the
conveying table 10, that is to say, the side opposite to the
endless belt 12 with respect to the conveying table 10. The imaging
unit 5 approaches the middle region (midstream) of the conveying
path. An opening 10o is formed in the central portion of the
conveying table 10 that corresponds to as the middle region of the
conveying path. A plate-shaped transparent member 21 that serves as
a portion of a case 20 of the imaging unit 5 is fitted in this
opening 10o. The transparent member 21 is formed for example with
sapphire glass or the like. The surface of the transparent member
21 is flush with the upper surface of the conveying table 10. The
coins 2 that are conveyed along the conveying path pass over the
transparent member 21. The location of imaging by the imaging unit
5 is at the transparent member 21 in the conveying path. When the
coins 2 being conveyed pass through the imaging location, the
imaging unit 5 images the coins 2.
The detecting unit 4 detects the coins 2 at the timing in which the
coins 2 being conveyed pass through the imaging location. The
detecting unit 4, in the illustrated example, includes a light
emitting element 31 and a light-receiving element 30 that form a
pair.
The light emitting element 31 is incorporated in the imaging unit 5
and emits light toward the transparent member 21. For example, an
LED (light emitting diode) or the like may be used as the light
emitting element 31. The light receiving element 30 is arranged on
the upper surface side of the conveying table 10, and opposite the
light emitting element 31. The light receiving element 30 receives
the light that is emitted from the light emitting element 31 and
passes through the transparent member 21. For example, a photodiode
or the like may be used as the light receiving element 30. When the
coin 2 is at the imaging location, the light from the light
emitting element 31 to the light receiving element 30 is blocked by
the coin 2. By detecting that the light reception by the light
receiving element 30 has been blocked, the detecting unit 4 detects
the coin 2 at the imaging location. The imaging unit 5 performs
imaging in synchronization with the detecting unit 4 detecting the
coin 2. In the illustrated example, the pair of the light emitting
element 31 and the light receiving element 30 are arranged in the
downstream region of the imaging location. However, the position of
the light emitting element 31 and the light receiving element 30 is
not particularly limited, and they may be arranged in the upstream
region of the imaging location.
The identifying unit 6 includes a memory 40, an imaging processing
unit 41, and an identification processing unit 42.
The memory 40 stores coin data including unevenness pattern data
relating the unevenness patterns of the surfaces of various coins.
The image processing unit 41 receives an input of the image data of
the surface of the coin 2 that has been imaged by the imaging unit
5. The image processing unit 41 analyzes this image data, and
produces imaged coin data that includes unevenness pattern data of
the imaged coin. The identification processing unit 42 receives an
input of the imaged coin data that is produced by the image
processing unit 41. The identification processing unit 42, by
extracting the coin data that matches the imaged coin data, from
the coin data of various coins that are stored in the memory 40,
identifies the coin 2 that has been imaged by the imaging unit
5.
The coin data and the imaged coin data may include, in addition to
the unevenness pattern data of the surfaces of the coins, for
example chromaticity data or brightness data relating to the color
of the surface of a coin. The chromaticity data can be used for
identifying coins together with the unevenness pattern. Also, it is
possible to detect the defaced state of the surface of a coin using
the chromaticity data and the brightness data.
FIG. 3 shows the imaging unit 5 of the coin identifying apparatus 1
in FIG. 1.
The imaging unit 5 that is shown in FIG. 3 is provided with a
surface light source 50, an imager 51, and a beam splitter 52.
The surface light source 50 emits with a constant output
illumination light that illuminates a surface of the coin 2 being
imaged. The illumination light is made to have a substantially
uniform illuminance over the entire region of the imaging location,
that is to say, over the whole surface of the transparent member
21. The detailed constitution of the surface light source 50 shall
be described below.
The imager 51 includes a solid state imaging element 53 and an
imaging optics (optical image forming system) 54. The solid state
imaging element 53 may be for example a CCD (charge coupled device)
image sensor or a CMOS (complementary metal oxide semiconductor)
image sensor. The imaging optics 54 forms an image on the image
reception area of the solid state imaging element 53. The imager 51
receives reflected light that is reflected by the surface of the
coin 2.
The beam splitter 52 transmits a portion of the incident light, and
reflects the remainder. As the beam splitter 52, a half mirror may
typically be used in which the ratio of transmittance and
reflectance are equivalent.
The beam splitter 52 is arranged at a location at which the
illumination light that is emitted from the surface light source 50
and the reflected light that is incident on the imager 51
intersect. The illumination light that is emitted from the surface
light source 50 is incident on the surface of the coin 2 via the
beam splitter 52, and the reflected light that is reflected by the
surface of the coin 2 is incident on the imager 51 via the beam
splitter 52.
In greater detail, the beam splitter 52 is positioned in the normal
direction of the surface of the coin 2 with respect to the coin 2.
The surface light source 50 is arranged in the optical path of the
light that advances in the normal direction of the surface of the
coin 2 and is reflected by the beam splitter 52. The imager 51 is
arranged in the optical path of light that advances in the normal
direction of the surface of the coin 2 and penetrates the beam
splitter 52. A portion of the illumination light that is emitted
from the surface light source 50 and incident on the beam splitter
52 is reflected by the beam splitter 52 to be incident on the
surface of the coin 2. A portion of the reflected light that is
reflected by the surface of the coin 2 and incident on the beam
splitter 52 penetrates the beam splitter 52 to be incident on the
imager 51. That is to say, this imaging unit 5 images by coaxial
epi-illumination (coaxial incident illumination).
The illumination light that is emitted from the surface light
source 50 includes parallel light and diffused light. An example of
the surface light source 50 that emits that kind of illumination
light is explained below.
FIG. 4 shows the surface light source 50 of the imaging unit 5 in
FIG. 3.
The surface light source 50 shown in FIG. 4 is a so-called
edge-light type surface light source, and has a light source
element 60, a light guide plate 61, and a diffusion film 63.
As the light source element 60, a cold cathode tube, a white LED or
the like that emits white light, for example, may be used. The
light source element 60 is arranged along a side face of the light
guide plate 61. If data relating to the color of the surface of a
coin (chromatic data and brightness data) is not required in the
identification of coins by the aforementioned identifying unit 6,
the light source element 60 may be a light source element that
emits monochromatic light.
The light guide plate 61 may be formed by acrylic, for example. A
fine prism pattern 62 is formed on the lower surface of the light
guide plate 61. Light that has been emitted from the light source
element 60 is incident on the side face of the light guide plate 61
and guided to inside the light guide plate 61, and reflected by the
prism pattern 62 on the lower surface of the light guide plate 61.
As a result, that light is emitted from the upper surface of the
light guide plate 61 in the normal direction of the upper surface
thereof.
The diffusion film 63 is layered on the upper surface of the light
guide plate 61, which is the emission face. The diffusion film 63
forms the emission face of the surface light source 50. A portion
of the light that is emitted from the upper surface of the light
guide plate 61 is dispersed by passing through the diffusion film
63.
The illumination light that is emitted from the surface light
source 50 that is constituted as described above includes the
above-mentioned parallel light that advances in the normal
direction of the emission face, and diffused light, by the property
of the light guide plate 61 and the property of the diffusion film
63 being combined. The diffused light includes light advancing
obliquely with respect to the normal direction of the emission
face. Including diffused light in the illumination light
contributes to equalization of the illuminance distribution at the
imaging location where this illumination light is to be irradiated.
This diffused light includes light that is obliquely incident on
the surface of the coin 2.
The surface light source 50 is arranged so that the emission face
the surface light source 50 intersects the optical path of light
that advances in the normal direction of the surface of the coin
and is reflected by the beam splitter 52. The parallel light that
is included in the illumination light is reflected by the beam
splitter 52, and is perpendicularly incident on the surface of the
coin 2. The diffused light that is included in the illumination
light is also reflected by the beam splitter 52 and incident on the
surface of the coin 2.
FIG. 5 schematically shows the illumination light that is incident
on the surface of the coin 2 and the reflected light that is
reflected by the surface of the coin 2.
The parallel light that is perpendicularly incident on the surface
of the coin 2 excluding the edge portion 2a of the unevenness
pattern of the surface of the coin 2 is reflected by the surface of
the coin 2, and most of that reflected light returns to the beam
splitter 52, and by penetrating the beam splitter 52, is received
by the imager 51. On the other hand, the parallel light that is
incident on the edge portion 2a of the unevenness pattern is
reflected by the edge portion 2a, but most of that reflected light
does not head to the beam splitter 52, so that the reflected light
that is reflected by the edge portion 2a and returns to the beam
splitter 52 remarkably decreases. Thereby, in the image that is
captured by the imager 51, contrast (a brightness difference) is
produced between the edge portion 2a of the unevenness pattern of
the surface of the coin 2 and the other portion of the surface of
the coin 2. In the identification of a coin by the identifying unit
6 mentioned above, the image processing unit 41 extracts the
unevenness pattern based on this contrast, and generates unevenness
pattern data.
Also, the diffused light that is incident on the surface of the
coin 2 raises overall the brightness of the surface of the coin 2.
As a result, the brightness of the entire surface of the coin 2 is
ensured even when the defacement of the surface of the coin 2 is
severe, or when the surface of the coin 2 is a diffusing surface.
Thereby, the contrast between the edge portion 2a of the unevenness
pattern of the surface of the coin 2 and the other portion of the
surface of the coin 2 that is produced by the parallel light
becomes distinct without blocked-up shadows. Therefore, it is
possible to reliably capture the unevenness pattern of the surface
of the coin 2 without being swayed by the nature of the surface
thereof, while holding constant the output of the surface light
source 50. Consequently, it is possible to maintain the
identification processing speed in the coin identifying apparatus 1
including the aforementioned imaging unit 5.
In the aforementioned example, taking the coin identifying
apparatus 1 as an example, the case was described of the imaging
unit 5 imaging coins. However, the subject is not limited to a
coin. For example, it is possible to have a disk-shaped article
having an unevenness pattern on a surface, with the reflectance of
the surface (specular reflectivity) approximating a coin, such as a
medal or the like, serve as the subject.
FIG. 6 shows a modification of the imaging unit 5 shown in FIG.
3.
The imaging unit 5' shown in FIG. 6 performs imaging by coaxial
epi-illumination. In the imaging unit 5', the arrangement of the
surface light source 50 and the imager 51 differ from the imaging
unit 5 that is shown in FIG. 3 in relation to the beam splitter 52.
The beam splitter 52 is positioned in the normal direction of the
surface of the coin 2 with respect to the coin 2. The surface light
source 50 is arranged in the optical path of the light that
advances in the normal direction of the surface of the coin 2 and
penetrates the beam splitter 52. The imager 51 is arranged in the
optical path of the light that advances in the normal direction of
the surface of the coin 2 and is reflected by the beam splitter 52.
A portion of the illumination light that is emitted from the
surface light source 50 and incident on the beam splitter 52
penetrates the beam splitter 52 to be incident on the surface of
the coin 2. A portion of the reflected light that is reflected by
the surface of the coin 2 and incident on the beam splitter 52 is
reflected by the beam splitter 52 to be incident on the imager
51.
In the imaging unit 5 shown in FIG. 3 and the imaging unit 5' shown
in FIG. 6, the imaging optics that is included in the imager 51 is
made to be a non-telecentric imaging optics. The surface light
source 50 emitting illumination light with a substantially uniform
illuminance over the entire surface of the coin 2 means that the
surface light source 50 projects onto the entire surface of the
coin 2. For example, in the imaging unit 5 shown in FIG. 3, it is
assumed as follows. The optical path length of the optical path P1
of the illumination light that is emitted from the surface light
source 50 and reaches the surface of the coin 2 is expressed as
"PL1". The optical path length of the optical path P2 of the
reflected light that is reflected by the surface of the coin 2 and
reaches the imager 51 is expressed as "PL2". The diameter of the
coin is expressed as "d". Also, the diameter of the surface light
source 50 is expressed as "D". In this case, the diameter D of the
surface light source 50 has a size of at least
"d.times.(PL1+PL2)/PL2".
FIG. 7 shows another example of the imaging unit. By giving the
same reference numerals to those elements that are shared by the
imaging unit 105 shown in FIG. 7 and the imaging unit 5 that is
shown in FIG. 3, the explanation is made simple or omitted.
The imaging unit 105 that is shown in FIG. 7 performs imaging by
coaxial epi-illumination. In this imaging unit 105, the object side
of the imaging optics (optical image forming system) 154 that is
included in the imaging unit 151 is made to be a telecentric
imaging optics. In this case, for the surface light source 150 to
project onto the entire surface of the coin 2, it is sufficient for
the diameter D of the surface light source 150 to be the same as
the diameter d of the coin. By using a telecentric imaging optics
for the imaging optics 154 of the imaging unit 151, it is possible
to miniaturize the surface light source 150, and therefore possible
to miniaturize the imaging unit 105. By miniaturizing the surface
light source 150 and the imaging unit 105, it is possible to
realize a reduction in power consumption, uniform illumination, and
lower costs. Moreover, by using a telecentric imaging optics, it is
possible to obtain a stable image with little distortion, and it is
possible to reduce unevenness of color and light quantity by the
angular distribution of the light rays that contribute to the image
formation becoming narrow.
FIGS. 8A to 8D show brightness distributions of images obtained by
imaging the surface of a coin. FIG. 9 shows the illuminance
distributions of the illumination light when imaging the images
with the brightness distributions of FIGS. 8A to 8D.
FIG. 8A shows a first brightness distribution of an image obtained
by imaging a nickel coin by the imaging unit 105 that emits
illumination light including parallel light and diffused light. The
nickel coin is such as a 100-yen coin in which the reflectance of
the surface is comparatively high. FIG. 8B shows a second
brightness distribution of an image obtained by imaging a copper
coin by the imaging unit 105. The copper coin is such as a 10-yen
coin in which the reflectance of the surface is comparatively low.
FIG. 8C shows a third brightness distribution of an image obtained
by imaging a nickel coin by an imaging unit that emits illumination
light including only parallel light. FIG. 8D shows a fourth
brightness distribution of an image obtained by imaging a copper
coin by an imaging unit that emits illumination light including
only parallel light. All of the first to fourth brightness
distributions are brightness distributions on one diameter of the
coin, and the edge portion of the unevenness pattern of the surface
of the coin corresponds to the valley portions of the brightness
distribution. FIG. 9 shows the illuminance distribution of the
illumination light of the imaging unit 105 that includes parallel
light and diffused light in the illumination light by a solid line
A. Also, FIG. 9 shows the illuminance distribution of the
illumination light of the imaging unit in which only parallel light
serves as the illumination light by a dashed line B.
In the fourth brightness distribution of the cooper coin in the
case of the illumination light being only parallel light (FIG. 8D),
blocked-up shadows occur due to the luminance of the surface of the
coin being low overall, and so the contrast between the edge
portion of the unevenness pattern and the other portion of the
surface of the coin becomes indistinct. In contrast to this, in the
second brightness distribution of the copper coin in the case of
the illumination light including diffused light (FIG. 8B), the
luminance of the surface of the coin is high overall due to the
diffused light, and so the contrast between the edge portion of the
unevenness pattern and the other portion of the surface of the coin
becomes distinct with no blocked-up shadows.
The average brightness difference between the first brightness
distribution of the nickel coin (FIG. 8A) and the second brightness
distribution of the copper coin (FIG. 8B) in the case of
illumination light including diffused light is smaller compared to
the average luminance difference between the third brightness
distribution of the nickel coin (FIG. 8C) and the fourth brightness
distribution of the copper coin (FIG. 8D) in the case of the
illumination light being only parallel light.
From the above, by emitting illumination light that includes
parallel light and diffused light on the surface of a coin, it is
possible to reliably capture the unevenness pattern of the surface
of a coin without being swayed by the nature of the surface
thereof, while keeping constant the output of the surface light
source 50.
As described above, in the present specification, an imaging unit
that images a subject having an unevenness pattern on a surface is
disclosed. The imaging unit includes: a surface light source that
emits with a constant output illumination light illuminating the
surface of the subject; an imager that receives reflected light
reflected by the surface of the subject; and a beam splitter that
is arranged at a location at which the illumination light emitted
from the surface light source and the reflected light incident on
the imager intersect with each other. The illumination light
emitted from the surface light source is incident on the surface of
the subject via the beam splitter. The reflected light reflected by
the surface of the subject is incident on the imager via the beam
splitter. The illumination light incident on the surface of the
subject includes parallel light that is perpendicularly incident on
the surface of the subject, and diffused light.
Moreover, in the imaging unit disclosed in the present
specification, the diffused light may include light that is
obliquely incident on the surface of the subject.
Moreover, in the imaging unit disclosed in the present
specification, the imager may include a telecentric imaging
optics.
Moreover, in the imaging unit disclosed in the present
specification, the subject may be a coin.
Moreover, as described above, in the present specification, a coin
identifying apparatus is disclosed. The coin identifying apparatus
includes: a conveying unit that conveys a coin; the above-mentioned
imaging unit imaging a surface of the coin that is conveyed by the
conveying unit; and an identifying unit that identifies the coin
based on an image acquired by the imaging unit.
While preferred embodiments of the invention have been described
and illustrated above, it should be understood that these are
exemplary of the invention and are not to be considered as
limiting. Additions, omissions, substitutions, and other
modifications can be made without departing from the scope of the
present invention. Accordingly, the invention is not to be
considered as being limited by the foregoing description, and is
only limited by the scope of the appended claims.
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